1. Field of the Invention
The present disclosure generally relates to a fixing unit of an image forming apparatus, and more particularly to a method of controlling a warming-up time of a fixing unit of the image forming apparatus.
2. Description of the Background Art
Image forming apparatuses using electrophotography may record an image on a recording medium using a procedure like the following: A rotating photoconductor, such as a photoconductor drum or a photoconductor belt, is charged by a charger; an electrostatic latent image is formed on the photoconductor by directing light onto the photoconductor; the electrostatic latent image is developed as a toner image by a development unit; the toner image is transferred to a recording medium (e.g., sheet, film, etc.) directly, or indirectly via an intermediate transfer member; the toner image is fixed on the recording medium by a fixing unit.
Such a fixing unit may include a fixing member and a pressing member setting a fixing nip therebetween, in which the pressing member presses against the heated fixing member. The recording medium is passed through the fixing nip to melt the toner with heat and fix the toner on the recording medium with pressure. The fixing member may be a fixing roller or a fixing belt provided with a heat source, such as a halogen heater or an induced heating coil (IH coil), used for heating the fixing member. The fixing roller may include the heat source inside the roller. The fixing belt may include the heat source in a roller used for extending the fixing belt, or around the fixing belt.
To save energy, the heat source may be de-energized (e.g., power supply is OFF) during a standby time (i.e., when an image forming process is not conducted). When the image forming process is resumed, the heat source is energized (e.g., power supply is ON) to heat the fixing member to a desired fixing temperature to prevent a fixing failure. Fixing process can be conducted most effectively at the desired fixing temperature.
The time required for heating the fixing member to the desired fixing temperature may be referred as a warming-up time. The warming-up time may be determined by a temperature mode, which determines a time that the fixing process can be conducted effectively based on a detection of actual temperature of the fixing member.
FIG. 1 shows example time-to-temperature profiles of the fixing member relative to the warming-up time for the fixing member. For example, in case of a line “a” of FIG. 1, the temperature of the fixing member reaches a designed fixing temperature Tf (e.g., 180 degrees Celcius) at a time tw (e.g., 30 seconds), and then it is determined that the fixing process can be conducted effectively at the time “tw” and after, and the power supply to the heat source is stopped.
However, a user may feel inconvenience and frustration with such a configuration using the temperature mode because the warming-up time may fluctuate in a given time range. For example, the warming-up time may fluctuate in a time range L as shown by a dot line “b” and a dot line “c” of FIG. 1.
In light of such fluctuation of the warming-up time using the temperature mode, a time mode may be employed for determining that the fixing process can be conducted effectively. In the time mode, it is determined that the fixing process can be conducted when the given time tw (e.g., 30 seconds) elapses after energizing the fixing member. Accordingly, in the time mode, the warming-up time can be set to a substantially constant value. Such warming-up time set by the time mode may be described as a feature of a product like “This machine can be ready for printing in a waiting time of “xx” seconds.” Although a fixing temperature of the fixing member may vary when the time mode is employed, such variation of the fixing temperature may not become a problem and the warming-up time can be set to a constant value.
Such conventional art can be found in JP-2005-345989-A, JP-3350315-B, JP-S62-70886-A, and JP-2004-240250-A, for example.
However, the time mode may have some drawbacks in some cases. For example, if the heat source is not supplied with enough electric power from a power source, the temperature of the fixing member may not reach the designed fixing temperature Tf at the warming-up time tw set by the time mode (see the broken line d of FIG. 1). Such a situation may occur when an input voltage to the heat source for some reason decreases. Because the time mode determines a start of fixing process using the time tw (see FIG. 1), the temperature of the fixing member may follow a temperature profile of the broken line “d” until “tw” and then the dotted line “e” when a sheet is fed to the fixing unit. Then the temperature of the fixing member becomes lower than a minimum fixing temperature Tm (e.g., 155 degrees Celcius), and thereby a fixing failure may occur.
There are several instances in which the heat source of the image forming apparatus might not get enough power to warm up the fixing member to the designated fixing temperature, such as when peripheral units are connected to the image forming apparatus or when the image forming apparatus needs to undergo an image adjustment operation. Both cases are described in detail below.
In general, the image forming apparatus may be connected to one or more peripheral units (e.g., a finisher, n automatic document feeder), and the image forming apparatus and the peripheral unit may be powered by a single power source. In such a system configuration, activation of the fixing unit may be conducted simultaneously with initialization of the peripheral unit, wherein the initialization may include resetting of a moving part to its home position in the peripheral unit, for example.
Accordingly, electrical power sufficient for the fixing process may not be supplied to the heat source from the single power source because the same single power source needs to supply electrical power used for initialization of the peripheral unit, by which the heat source may not generate sufficient heat energy for heating the fixing member. Accordingly, if the time mode is employed for the image forming apparatus that is connected to the peripheral unit, the temperature of the fixing member may not be increased to the desired fixing temperature using the time mode, by which a fixing failure may occur.
Further, an image forming apparatus may need an image adjustment operation when the image forming apparatus is activated after leaving the image forming apparatus in an un-used condition for a given time period or when a sensor value read by an environment sensor changes greatly because imaging condition (e.g., toner concentration, image writing timing) may change. To maintain an image quality at a higher quality level, the image adjustment operation (e.g., image concentration adjustment operation, color-position displacement correction of image forming engine) may be conducted when the image forming apparatus is activated. Accordingly, electrical power sufficient for the fixing process may not be supplied to the heat source from the single power source because the same single power source need to supply electrical power used for the image adjustment operation, by which the heat source may not generate sufficient heat energy for heating the fixing member. Accordingly, if the time mode is employed for the image forming apparatus which needs the image adjustment operation, the temperature of the fixing member may not be increased to the desired fixing temperature, by which a fixing failure may occur.